A series of silver coordination polymers constructed from flexible bis(benzimidazole) ligands and different carboxylates

In this article, eight new silver coordination polymers constructed from two structurally related ligands, 1,1′-(1,4-butanediyl)bis(2-methylbenzimidazole) (bbmb) and 1,1′-(1,4-butanediyl)bis(2-ethylbenzimedazole) (bbeb), have been synthesized: [Ag(L1)(bbmb)]·C2H5OH·H2O (1), [Ag(L2)(bbmb)]·C2H5OH (2), [Ag(L3)(bbmb)] (3), [Ag2(L4)(bbmb)2]·C2H5OH (4), [Ag(L2)(bbeb)]·C2H5OH (5), [Ag(L5)(bbeb)]·CH3OH (6), [Ag2(L6)2(bbeb)]·H2O (7), and [Ag2(L7)(bbeb)2]·4(H2O) (8), where L1 = benzoate anion, L2 = p-methoxybenzoate anion, L3 = 2-amino-benzoate anion, L4 = oxalate anion, L5 = cinnamate ainon, L6 = 3-amino-benzoate anion, and L7 = fumaric anion. In 1–3, 5 and 6, the bidentate N-donor ligands (bbmb and bbeb) in trans conformations bridge neighboring silver centers to form 1D single chain structures. The carboxylate anions are attached on both sides of the chains. Moreover, 1 and 3 are extended into 2D layers, while 2 and 6 are extended into 3D frameworks through π–π interactions. In 4, the bbmb ligands bridge adjacent Ag(I) centers to form –Ag–bbmb–Ag– chains, which are further connected by L4 anions to form a 2D layer. The resulting layers are extended into 3D frameworks through strong π–π interactions. In 7, the N-donor ligands (bbeb) in trans conformations bridge two silver centers to generate a [Ag2(bbeb)]2+ unit. The adjacent [Ag2(bbeb)]2+ units are further connected via the L6 anions to form a 1D ladder chain. Moreover, the structure of compound 7 is extended into a 3D framework through hydrogen bonding and π–π interactions. In 8, two Ag(I) cations are bridged by two bbeb ligands in cis conformations to form a [Ag2(bbeb)2]2+ ring, which are further linked by L7 anions to generate a 1D string chain. Furthermore, the hydrogen bonding and π–π interactions link L7 anions to form a 2D supramolecular sheet. Additionally, the luminescent properties of these compounds were also studied.

The 1D chain structures of the complexes are mainly determined by the nature of the secondary ligands because of their strong coordination ability for the Ag(I) ion.Figure optionsDownload as PowerPoint slideHighlights
► The structures of carboxylate anions are the reason for the structural differences.
► The chain structures are mainly determined by the nature of the secondary ligands
► The bbmb and bbeb coordinate to Ag(I) ion in a linear mode to form a chain.